S-4 · S4
Andarine (S-4, also known as GTx-007) is a non-steroidal selective androgen receptor modulator (SARM) originally developed by Kaken Pharmaceuticals and later by GTx, Inc. for the treatment of muscle wasting, osteoporosis, and benign prostatic hyperplasia. Structurally it is a derivative of bicalutamide (an anti-androgen) modified to produce partial-agonist activity at the androgen receptor in muscle and bone tissue while retaining anti-androgenic activity in the prostate.
Short half-life (~4-6 hours) means most users split the daily dose 2-3 times for more stable coverage. A common protocol is 25mg 2x daily (50mg total) or 15mg 3x daily (45mg total). Plan pre-cycle and post-cycle bloodwork (testosterone, LH, FSH, lipid panel, ALT/AST). Plan PCT for cycles over 6 weeks or doses over 25mg total daily.
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
Andarine binds the androgen receptor (AR) as a tissue-selective partial agonist with a particularly strong selectivity profile for muscle and bone versus prostate and seminal vesicle tissue. As a bicalutamide derivative, it retains some anti-androgen character in prostate tissue - preclinical models show reduced prostate weight alongside increased muscle mass, which is the opposite of what traditional AAS produce.
As a non-steroidal compound it does not aromatize to estrogen and does not convert to DHT. This eliminates aromatase and 5-alpha-reductase-driven side effects at standard doses. HPT-axis suppression is generally milder than RAD-140, LGD-4033, or S-23 at comparable doses but still meaningful at higher doses or longer cycles. PCT is recommended for cycles over 20mg/day or longer than 6 weeks.
The defining side effect of andarine is the visual disturbance. Androgen receptors are expressed in the retina, and andarine's binding there produces a dose-dependent yellow tint to vision and impaired night vision / slower dark adaptation. Users frequently describe it as 'looking through yellow-tinted glasses' at night. The effect is reversible on discontinuation - vision typically returns to baseline within 1-4 weeks off. This side effect is essentially unique to andarine among common SARMs and is the main reason it has fallen out of favor in the community in recent years.
First 1-2 weeks: subtle strength and hardening onset. Vision changes may begin to appear at higher doses (50mg+ daily).
Weeks 3-5: visible hardening and muscle definition, vision effects typically well-established. Mid-cycle bloodwork appropriate.
Weeks 6-8: peak benefits. Cycle end recommended by week 8 to give vision effects time to resolve. PCT begins after last dose for cycles over 6 weeks or higher doses.
Each reference below was re-fetched from its PubMed record, and the quoted sentence was confirmed to appear in that abstract and to support the claim it sits under. Follow any of them to read the source.
Mechanism boundary: S-4 acted as a tissue-selective SARM with strong skeletal-muscle and bone effects and minimal prostate effect in orchidectomized rats.
In summary, the strong anabolic effects of S-4 in skeletal muscle, bone, and pituitary were achieved with minimal pharmacologic effect in the prostate.
Evidence scope. Animal (orchidectomized rats); preclinical only, no human data implied.
Preclinical effect: S-4 maintained bone mineral density and strength while reducing body fat in ovariectomized rats.
We found that S-4 treatment maintained whole body and trabecular BMD, cortical content, and increased bone strength while decreasing body fat in these animals.
Evidence scope. Animal (ovariectomized rats); preclinical only.
Claims we could not support
No abstract we checked supports these for this molecule at this route. That is not the same as saying they are false — it marks where the evidence is missing.
Dose/route: 25 mg orally 2-3x/day or 25-50 mg/day. The checked exact-molecule abstracts were animal or analytical studies; none administered the displayed oral human regimen.
Primary safety concern: yellow-tinted vision / impaired night vision. No checked exact-molecule PubMed abstract directly documented this claimed human visual adverse effect. General SARM safety or anecdotal reports were not substituted.
High oral bioavailability
Per dose - supports 2-3x daily dosing
Hepatic metabolism. Renal excretion of metabolites.
Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and light. Keep capsules in original container with desiccant when available. Liquid suspensions should be kept sealed and used within 12 months of opening. Shelf life typically 2-3 years from manufacture date for capsules, 1-2 years for liquid. Keep out of reach of children.
Andarine (S-4) is NOT FDA-approved for any indication. Classified as a research chemical in the United States - not a controlled substance federally as of this writing, but banned by WADA, USADA, the NCAA, and most professional sports leagues. FDA has issued warnings against SARM sales as over-the-counter dietary supplements. Some US states have introduced legislation restricting SARM sales. Use falls outside regulated medical practice.
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